MMSE decision-feedback equalizers and coding. I. Equalizationresults

The minimum mean-squared-error decision-feedback equalizer (MMSE-DFE) has properties that suggest that it is a canonical equalization structure for systems that combine equalization with coded modulation. The structure and performance of the MMSE-DFE are succinctly derived using linear-estimation-theoretic principles in this first part of this two-part paper. The front-end of the MMSE-DFE, called the “mean-square whitened matched filter” (MS-WMF), is preferable in some ways to a matched filter or a whitened matched filter as a canonical receiver front end. In a coded system, the feedback filter of the MMSE-DFE may be implemented in the transmitter using precoding. The MMSE-DFE can perform significantly better than a zero-forcing decision-feedback equalizer, particularly at moderate-to-low SNR's and on severe-ISI channels. The MMSE-DFE is biased. The optimum unbiased MMSE-DFE is the MMSE-DFE with the bias removed. Removing bias improves error probability, but reduces the SNR to SNR_MMSE-DFE,U=SNR_MMSE-DFE-1. It is shown that this SNR relationship is a particular case of a very general result and that SNR_MMSE-DFE,U gives a more realistic estimate of SNR. The results are extended to partial response equalization and to equalization with correlated inputs in an appendix     

Coherent lidar airborne wind sensor II: flight-test results at 2 and 10 νm

The use of airborne laser radar (lidar) to measure wind velocities and to detect turbulence in front of an aircraft in real time can significantly increase fuel efficiency, flight safety, and terminal area capacity. We describe the flight-test results for two coherent lidar airborne shear sensor (CLASS) systems and discuss their agreement with our theoretical simulations. The 10.6-μm CO(2) system (CLASS-10) is a flying brassboard; the 2.02-μm Tm:YAG solid-state system (CLASS-2) is configured in a rugged, light-weight, high-performance package. Both lidars have shown a wind measurement accuracy of better than 1 m/s.     

A reactive molecular dynamics model of thermal decomposition in polymers: I. Poly(methyl methacrylate)

The theory and implementation of reactive molecular dynamics (RMD) are presented. The capabilities of RMD and its potential use as a tool for investigating the mechanisms of thermal transformations in materials are demonstrated by presenting results from simulations of the thermal degradation of poly(methyl methacrylate) (PMMA). While it is known that depolymerization must be the major decomposition channel for PMMA, there are unanswered questions about the nature of the initiation reaction and the relative reactivities of the tertiary and primary radicals formed in the degradation process. The results of our RMD simulations, performed directly in the condensed phase, are consistent with available experimental information. They also provide new insights into the mechanism of the thermally induced conversion of this polymer into its constituent monomers.     

Neurochemical alterations in asymptomatic abstinent cocaine users: a proton magnetic resonance spectroscopy study

Cocaine can cause a variety of neuropsychiatric and neurobehavioral complications; however, it is uncertain whether cocaine causes persistent cerebral structural and neurochemical abnormalities in asymptomatic users. We studied 52 African-American men (26 human immunodeficiency virus-negative asymptomatic heavy cocaine users and 26 normal subjects). Ventricle-to-brain ratio (VBR) and white matter lesions (WML) were quantified on magnetic resonance imaging. N-acetyl-containing compounds (NA), total creatine, choline-containing compounds, myo-inositol, and glutamate + glutamine were measured with in vivo proton magnetic resonance spectroscopy, VBR and WML were not significantly different in the cocaine users compared to the normal controls. Elevated creatine (+7%; p = .05) and myo-inositol (+18%; p = .01) in the white matter were associated with cocaine use. NA, primarily a measure of N-acetyl aspartate and neuronal content, was normal. Normal NA suggest no neuronal loss or damage in the brain regions examined in these cocaine users. Therefore, we conclude that neurochemical abnormalities observed might result from alterations in nonneuronal brain tissue.     

Reactivity of antibodies against conserved regions of pilins of Haemophilus influenzae type b

To identify epitopes on pilins of Haemophilus influenzae type b (Hib) that may also be immunologically available on assembled pili, antisera were developed against eight synthetic peptides that represent conserved and hydrophilic regions of Hib pilin. Seven of the eight peptides were immunogenic. Binding of the anti-peptide antibodies to purified pili of Hib strain Eagan was weak. However, when the purified pili were denatured by heating, binding of the anti-peptide antibodies improved considerably, suggesting that the epitopes defined by the peptides were more available for anti-peptide antibody binding on the denatured pilins than on purified pili. On Western blot analysis, strain variation was seen in the binding of some of the anti-peptide antibodies, notably those directed against peptides in the N-terminal half of the pilin. Thus, when pilins are assembled into pili, the epitopes defined by the seven immunogenic peptides appear to be altered so that binding of the anti-peptide antibodies is greatly reduced.     

Characterization and distribution of esterase activity in activated sludge.

The location and activity of esterase enzymes in activated sludge from three municipal wastewater treatment plants were characterized using model substrates and denaturing and non-denaturing polyacrylamide gel electrophoresis (PAGE) of particulate, freeze-thaw (primarily periplasmic enzymes and those associated with outer cell surfaces) and extracellular fractions of activated sludge bacteria. Particulate and freeze-thaw fractions had a similar spectrum of substrate specificity and contained significant levels of protein and esterase activity against model substrates, C2-C18 monoesters of p-nitrophenol and C2-C8 diesters of fluorescein. Esterase activity was highest with substrates that had short alkyl chains (C4) and decreased as the chain lengths increased beyond C8. Extracellular fractions contained very low levels of protein (<0.1 mg/l) and showed no esterase activity against any of the model substrates tested. Multiple bands were observed upon analysis of particulate and freeze-thaw fractions by non-denaturing PAGE in combination with activity staining using various alpha-naphthol ester substrates (C2-C8). Our results indicate that esterase enzymes in activated sludge are fairly diverse from a structural standpoint but exhibit a high level of functional redundancy, with different enzymes catalyzing the same reactions in different sludges. Extracellular esterase activity was totally absent for the substrates we tested and the esterase activity that we observed was closely linked to a particulate floc or cellular material.     

Effect of Gaseous Ozone on Papaya Anthracnose

Anthracnose caused by the fungus Colletotrichum gloeosporioides is considered as one of the most devastating postharvest disease of papaya. The aim of this study was to evaluate the effectiveness of gaseous ozone as a potential antifungal preservation technique to overcome anthracnose disease of papaya during cold storage. Different concentrations of ozone (0 (control), 0.04, 1.6, and 4 ppm) were applied for various exposure durations (48, 96, and 144 h). Radial mycelia growth and conidial germination were evaluated in vitro after fungal exposure to the different levels and durations of ozone. Significant inhibition in radial mycelia growth of C. gloeosporioides was observed (p?<?0.05) in all ozone treatments as compared to the control during 8 days of incubation at room temperature (25?±?3 °C). Ozone treatment of papaya fruit with 1.6-ppm ozone for 96 h delayed and simultaneously decreased the disease incidence to 40 % whereas disease severity was rated at 1.7, following 28 days of storage at 12?±?1 °C and 80 % relative humidity. The scanning electron microscopy showed that 4-ppm ozone caused disintegration of spore structure and did not affect the cuticular surface of fruit. Thus, ozone fumigation can reduce postharvest losses of papaya caused by anthracnose.     

V.92: the last dial-up modem?

Ever since the first dial-up modems appeared in the 1960s, their obsolescence has been repeatedly predicted. However, contrary to such predictions, dial-up modems thrived in the 1980s and 1990s as a result of the slow rollout of residential digital services and the unprecedented growth of internet and remote access. Since the first 300 b/s dial-up modem standard (V.21), modem speeds have increased steadily. Most recently, International Telecommunications Union (ITU) Recommendation V.90 (1998) takes advantage of the direct digital-network connection of an internet service provider (ISP) remote-access server to achieve speeds of more than 50 kb/s downstream (from ISP to a user). However, for upstream transmission (from a user to ISP), V.90 employs the older V.34 modulation (1994), which typically delivers on the order of 30 kb/s. A new ITU modem standard called V.92 increases upstream rates to above 40 kb/s, again by taking advantage of pulse code modulation connections. In this paper, we present the transmission scheme that has been adopted for V.92. It involves a generalization of Tomlinson-Harashima precoding. We predict that V.92 will be the last dial-up modem standard. However, we have to wonder whether we might be falling into the same trap into which many others have fallen in the past. The future will be the judge!.     

Slow second-order reactions in a deflected buoyant jet

An integral method including the entrainment hypothesis of Hoult, Fay and Forney (1969) is used to predict the concentration of product formed in a buoyant jet in a crossflow. The analysis is restricted to a slow, irreversible, second-order reaction with premixed reactants. Reliable laboratory data are presented for the oxidation of nitric oxide by the reaction 2NO + O₂ → 2NO₂ with excess O₂ and these results are correlated with the theory. Additional measurements are recorded to provide information on the magnitude of the turbulent parameters necessary for proper closure of the rate expressions.